As a method of performing crowning processing on end faces of a roller, there is known processing using a double-head surface grinder and processing using a cup grinding stone. As a method of feeding a workpiece, it is general to feed a workpiece using a carrier (rotary carrier) having pockets arranged concentrically in an outer rim portion of a disk thereof.
However, the size of the carrier pocket is larger than the diameter of the workpiece, and hence a “clearance” is formed between the two (between the workpiece and the pocket), with the result that the processing position and the posture are unstable. Further, the carrier itself does not have any action of controlling the rotation of the workpiece, and the rotation depends entirely on processability of the grinding stone, with the result that stable rotation cannot be attained. Hence, uniform processing cannot be performed in a circumferential direction and runout accuracy of end faces cannot be obtained.
Therefore, in recent years, there have been developed products that enable both the end faces of the workpiece to be ground with high accuracy (Patent Literature 1 and Patent Literature 2).
Patent Literature 1 describes a double-head surface grinder. As illustrated in FIG. 11, the double-head surface grinder includes a pair of ring-like grinding stones 1, a carrier 4 arranged between the grinding stones 1, and a ring-like guide member 5 arranged on an outer periphery side of the carrier 4.
The carrier 4 has pockets 3 formed in its radially-outer surface and arranged at a predetermined pitch along the circumferential direction. Workpieces W are fitted to the pockets 3. Further, the workpieces W can be held in the pockets 3 by the guide member 5.
In this case, the guide member 5 is arranged by decentering an axis O1 of the guide member 5 from a carrier axis O by a decentering amount A so that a gap between a guide surface (radially-inner surface of the guide member 5) and the carrier 4 is smaller on a processing position H side and larger on a loading position X side opposite to the processing position H. In this case, the guide member 5 holds, together with the pocket 3, the workpiece W fed to the pocket 3 of the carrier 4 at the loading position X, and guides the workpiece W from the loading position x to an unloading position Y through the processing position H while rotating the workpiece W about its axis along with the rotation of the carrier 4.
The gap between the guide surface and the carrier 4 is larger on the loading position X side, and hence the workpiece W can be fed to the pocket 3 easily and quickly. Further, the gap between the guide surface and the carrier 4 is smaller on the processing position H side, and hence the stability of the posture of the workpiece W is enhanced, with the result that both the end faces of the workpiece W can be ground with high accuracy.
As illustrated in FIG. 12, the product described in Patent Literature 2 includes a rotatable inner disk 6, a cage 9 holding a plurality workpieces substantially equiangularly on a radially-outer portion having pocket portions 8 and a drive belt 10 stretched over radially-outer portions of the plurality of workpieces W held by the inner disk 6 and the cage 9.
Further, by rotationally driving the inner disk 6 and the drive belt 10 in opposite directions, rotational motion is applied to the workpieces W, and further, by rotating the cage 9, revolutional motion is applied to the workpieces W.
Further, cup grinding stones for processing the end faces of the workpiece W are pressed at two positions against the end faces of the workpiece W at a fixed pressure from opposite directions, and hence both the end faces of the workpiece W can be processed.
Accordingly, in the processing apparatus illustrated in FIG. 12, the end faces of the workpiece can be processed by using the elastic processing tool while rotating and revolving the workpiece. Thus, the rotation of the workpiece is kept stable, and the runout accuracy of the roller end faces can be enhanced.
By the way, there is conventionally a tangential feed grinding method using a centerless grinder (Patent Literature 3). In this case, as illustrated in FIG. 13, the centerless grinder includes a grinding wheel 11, a regulating wheel 12, and a carrier 13. Further, the centerless grinder includes a rotation shaft 12a and a rotation shaft 13a for supporting and driving the grinding wheel 11 and the carrier 13, respectively. Further, at least one end face 15 of a workpiece W fitted into a workpiece pocket 14 of the carrier 13 is in a state of being closed completely or partially.